Many nonwoven fabrics are interfilamentarily bonded to impart integrity to the fabric. While there are several bonding techniques available, thermal bonding processes prevail in the nonwovens industry both in volume and time devoted to the research and development of new products. These processes have gained wide acceptance due to simplicity and many advantages over traditional chemical bonding methods. Attractive features include low energy and raw material costs, increased production rates, and product versatility. Chemical simplification, since binders are not used, reduces concerns over the environment.
Thermal bonding processes involve the incorporation of a heat sensitive material into a web using traditional web forming techniques. Heated rolls in calender bonding or hot air in hot air bonding bring the web to a temperature at or near the melting point of this material. The molten mass flows and a glue-like bond forms to provide strength to the nonwoven. The bonding agent in many cases is a fusible fiber blended with a matrix fiber or used alone in the base web.
U.S. Pat. No. 2,277,049 to Reed introduced the idea of using fusible fibers to make nonwoven fabrics. He proposed blending fusible and nonfusible fibers of similar denier and cut length and treating the web with either solvent or heat. The fusible fibers become tacky and act as a binder. A nonwoven fabric results after pressing and cooling the tacky web.
A goal in manufacturing nonwoven fabrics is to make them both absorbent and strong. To accomplish this goal, blends of materials are used. Commonly, rayon or other cellulosics are used for absorbency and polypropylene or other polyolefins are used for strength. In cellulosic/polyolefin blend nonwovens, as the percentage of polyolefin increases, the absorbency decreases. Vice versa, as the percentage of cellulosic increases, the fabric strength decreases. There is, therefore, an inherent dilemma in manufacturing nonwovens which are both absorbent and strong.
One solution to the dilemma is spun-laced fabrics. Spun-laced fabrics are made by mechanical entanglement of filaments with water jets. The resulting fabric is strong and absorbent, but very expensive.
Strong and absorbent nonwovens may be prepared using latex resin as a bonding agent. The use of latex raises the specter of environmental problems. Also, the latex must be dried at additional expense and complication to the process.